1. Field of the Invention
The present invention relates to a charged particle beam exposure system and a method of controlling the system, and particularly to a system for emitting and deflecting an electron beam toward an object to draw semiconductor integrated circuit patterns on the object placed on a stage that is continuously moved, and a method of controlling the system.
2. Description of the Related Art
To densely integrate LSIs on a chip, fine LSI patterns are frequently drawn by using, instead of a photolithography technique, an exposure technique employing charged particle beams such as electron beams and X ray beams.
To improve the speed and efficiency of the pattern drawing, a continuously moving stage exposure method has been developed. This method continuously moves a stage on which an object to be exposed is placed. When shifting an electron beam between main exposure regions on the object, the method activates an electromagnetic deflector is activated to electromagnetically deflect the electron beam, and when drawing patterns in each subregion, an electrostatic deflector is activated to electrostatically deflect the electron beam.
In shifting the electron beam between the regions, it takes time to stabilize a main deflector amplifier due to inductance of the electromagnetic deflector. It is necessary, therefore, to set a predetermined wait time depending on a jump quantity of the electron beam between the regions before starting the pattern drawing with the electron beam.
Unlike a conventional step-and-repeat exposure method, the continuously moving stage exposure method periodically reads a stage position and feeds the read data back to a deflection processing system. Accordingly, it may happen that the stage position is read just before the elapse of the wait time to destabilize the electromagnetic deflector even after the wait time. This may fluctuate the pattern drawing and thus deteriorate the reliability of the exposure system.
It is required, therefore, to provide a system and a method that correctly starts drawing patterns in response to not only the wait time for stabilizing the electromagnetic deflector but also another wait time related to a period of reading and controlling the stage position, to improve the reliability of the continuously moving stage exposure method.
FIG. 4(a) to 4(c) are the block diagram showing an electron beam exposure system according to a prior art.
This system emits an electron beam 1a to draw an LSI pattern on an object 8 such as a semiconductor wafer. The system comprises an electron gun 1, an electrostatic deflector (a subdeflector) 2, an electromagnetic deflector (a main deflector) 3, a subdeflector driver 4, a main deflector driver 5, a length measuring laser unit 6A, a stage moving unit 6B, a stage controller 6C, a stage position correction unit 6D, a stage 6E, a central processing unit (CPU) 7, etc.
The main deflector driver 5 comprises a main deflector data buffer 5A, main deflector position setting circuit 5B, an addition/output circuit 5C, a second correction circuit 5D, a wait time generator 5E, a main deflector amplifier 5F, a field memory 5G, D/A converters DAC2 and DAC3, amplifiers AMP1 and AMP2, etc.
The exposure object 8 on the stage 6E is continuously moved by the stage moving unit 6B. The electron beam 1a from the electron gun 1 is deflected toward the exposure object 8 by the electrostatic deflector 2 and electromagnetic deflector 3.
To draw a pattern in a subregion of the exposure object 8, subdeflector data SD is supplied to a subdeflector data buffer 4A and a subdeflector pattern generation 4B of the subdeflector driver 4. The data SD is processed through a first correction circuit 4C, a D/A converter DAC1, the field memory 5G, and a subdeflector amplifier 4D, to provide a subdeflector signal SSD to the electrostatic deflector 2, which electrostatically deflects the electron beam 1a.
The timing of starting the pattern drawing in the subregion is controlled according to a drawing start signal S31 provided by the wait time generator 5E of the main deflector driver 5.
When the stage 6E is moved between main regions of the exposure object 8, main deflector data MD is supplied to the main deflector data buffer 5A of the main deflector driver 5. The main deflector position setting circuit 5B sets a deflective target position and provides main deflector data MD11 related to the deflective target position. The addition/output circuit 5C processes the main deflector data MD11 and stage position data STD provided by the stage controller 6C. The second correction circuit 5D corrects a stage moving quantity and a deflection quantity up to the deflective target position and provides corrected main deflector data MD12. The main deflector amplifier 5F processes the corrected main deflector data MD12 and provides a main deflector signal S21 to the electromagnetic deflector 3, which then electromagnetically deflects the electron beam 1a.
Meanwhile, the wait time generator 5E receives a main deflector set signal S11 (FIG. 7) contained in the corrected main deflector data MD12 provided by the second correction circuit 5D, and according to the signal S11, generates a pulse signal PS corresponding to the deflection quantity (jump quantity) of the electron beam 1a. The pulse signal PS defines a wait time T for stabilizing the main deflector amplifier 5F. The signal PS will be at a high (H) level for a waiting operation and a low (L) level for a non-waiting operation.
With this arrangement, the electron beam 1a is deflected toward the continuously moving object 8 to draw LSI patterns on the object.
When the electron beam 1a is moved from an optional region to another region on the continuously moving object 8 to continue the pattern drawing, the timing Tx of starting the pattern drawing is synchronized with the low level of the drawing start signal S31, which falls to the low level after the wait time T as shown in FIG. 5.
Accordingly, depending on a period of reading the stage position and the wait time T, it may happen that a pulse (4) of the main deflector set signal S11 contained in the corrected main deflector data MD12 is provided to the main deflector amplifier 5F just before the elapse of the wait time T, and the drawing start signal S31 is provided to a subdeflector pattern generator 4B of the subdeflector driver 4 just after the wait time T. This is understood to happen due to a slight control difference between an electromagnetic deflector feedback control system and an electrostatic deflector feedback control system.
Here, the electromagnetic deflector feedback control system comprises the main deflector driver 5, length measuring laser unit 6A for measuring the position of the continuously moving stage 6E, and parts of the stage controller 6C involving a laser counter 61, an offset register 62, an adder 63, a stage position register 64, and a subtracter 66. The electrostatic deflector feedback control system comprises the length measuring laser unit 6A, laser counter 61, subtracter 67, third correction circuit 68, and D/A converter DAC4.
Due to the slight control difference between these two feedback control systems, the pattern drawing in a subregion of the object 8 may be started even if the main deflector amplifier 5F is not yet stabilized, i.e., even if the main deflector signal S21 from the main deflector amplifier 5F is in an unstable area 10 shown in FIG. 5. If this happens, a deformed pattern may be drawn on the exposure object 8, what deteriorates the reliability of the continuously moving stage exposure system.